Constructing local hidden variable (LHV) and local hidden state (LHS) models for entangled quantum states is a challenging problem, with implications for the foundations of quantum theory and for quantum information processing. Here we presented a simple method for building LHV and LHS models, applicable to any entangled state and considering continuous sets of measurements (a schematic view of the onion structure of such sets are shown in the figure). This leads to a sequence of tests which, in the limit, fully captures the set of quantum states admitting a LHV and a LHS model. We illustrated the practical relevance of these methods with several examples.

Tree ring series were collected from the vicinity of a Hungarian radioactive waste treatment and disposal facility and from a distant control background site, which is not influenced by the radiocarbon discharge of the disposal facility but it represents the natural regional 14C level. The 14C concentration of the cellulose content of tree rings was measured by AMS. Data of the tree ring series from the disposal facility was compared to the control site for each year. The results were also compared to the 14C data of the atmospheric 14C monitoring stations at the disposal facility and to international background measurements. On the basis of the results, the excess radiocarbon of the disposal facility can unambiguously be detected in the tree from the repository site.

Activation cross sections of proton induced reactions on gold for production of 197m,197g,195m,195g,193m,193g,192Hg, 196m,196g(cum),195g(cum),194,191(cum)Au, 191(cum)Pt and 192Ir were measured up to 65 MeV proton energy, some of them for the first time. Two stacks containing the Au and monitor as well as energy degradation and recoil catcher foils were irradiated at an external beam line of the Cyclone110 cyclotron of the Université Catholique in Louvain la Neuve (LLN) with a 65 MeV proton beam. An additional stack was irradiated at the external beam line of VUB CGR 560 cyclotron (Brussels) with a 33.7 MeV incident proton beam. The stacks were separated and each foil was measured by gamma-spectrometer several times to follow the decay of the produced radioisotopes.

From the measured activities, by using the irradiated parameters (measured and adjusted by using the monitor reactions) excitation functions were deduced for the above mentioned radioisotopes. The new data are in acceptably good agreement with the recently published earlier experimental data in the overlapping energy region. The experimental data were also compared with the predictions of the TALYS 1.6 (results in TENDL-2015 on-line library) and EMPIRE 3.2 nuclear reaction model codes.

From our new experimental cross sections integral yield curves were calculated and compared with the previous literature values. Two fields of applications of the produced radioisotopes were discussed in detail: Thin Layer Activation (TLA), which is mainly used for measurement of wear, corrosion and erosion of different materials, as well as beam monitoring in the higher proton energy region.

In the conclusion it was emphasized that our results are partly new and in the overlapping energy region show good agreement with the previous literature data. The predictions of the nuclear reaction model codes are still far from perfect but show significant improvements in some cases.

The N-party W-type state plays a crucial role in quantum networks, in quantum memories in particular: https://en.wikipedia.org/wiki/W_state. It can be generated by delocalizing a single photon over several paths via a sequence of beam splitters (see a sketch of the figure).

In the present work, researchers from MTA Atomki investigate the nonlocal properties of the W-type states against particle loss. In case of three parties, if only two parties detect photons (i.e. the third photon is lost), it is an open problem whether the two-party state is nonlocal. In case of general N, one may inquire what is the minimal number of particles that must be removed from the W-type state so that the resulting state becomes local. This number is found to be bigger than (2N/5) for large N. This result supports the high persistency of W-type states under particle loss, which is a useful property in present-day quantum technologies.

EPR steering inequalities with communication assistance

In a joint collaboration of the University of Debrecen and MTA Atomki, researchers investigated the amount of resources to simulate a bipartite hybrid quantum scenario. The scenario involves a trusted system and an untrusted part (a so-called black box system), which share a bipartite entangled quantum state. Local quantum measurements are carried out on the untrusted part, which influence the trusted part by remotely steering its quantum state. This "spooky action at a distance" is first described by Schrödinger in 1936 and has been put on a firm basis by Wiseman et al. in the context of quantum information in 2007. Since then, numerous experiments have confirmed the above phenomenon.

In this paper, the quantum steering is simulated classically by substituting entanglement with classical communication between the untrusted and trusted systems. As a main result, it is proven that infinite amount of classical communication is required from an untrusted party to a trusted party in order to simulate steering correlations arising from a pure two-qubit entangled state. This result nicely demonstrates the power of quantum entanglement over the use of classical resources such as classical communication.